Bead area durability is one of the concerns of the tire industry. A conventional tire bead portion 100 is illustrated in FIG. 7. What is conventionally considered the main portion 104 of a carcass reinforcing ply extends radially inward toward the tire rim and is turned about an inextensible bead core 106 to form a carcass ply turnup 108. The carcass ply turn up 108 extends at a single angle μ relative to a radial line tangent to the axially outermost point of the bead core 106 and parallel to the tire equatorial plane.
Due to the configuration and nature of the radial carcass, when a tire is expanded, the main portion of the carcass is put under tension, pulling the carcass main portion 104 radially upward and the carcass turn up 108 radially inward. After inflation and during operation of the tire, when the tire is under deflection, the carcass ply is subject to bending forces and the carcass main portion 104 moves radially inward while the carcass turn up 108 moves radially and axially outward. During both tension and deflection, the rubber surrounding the carcass main portion 104 and the carcass turn up 108, due to the adhesion relationship between the rubber and the reinforcing cords of the ply, also is forced to move and the rubber is stressed. The movement of the carcass ply and the surrounding rubber may result in cracking of the rubber in the tire bead portion, decreasing durability of the tire.
Other attempts have been made to improve the durability of the bead portion. U.S. Pat. No. 6,260,597 (Miyazono) discloses a pneumatic tire having multiple cord reinforced chafer layers in the bead portions outward of a carcass ply. Axially outward of the carcass ply turnup, the terminal ends of the chafer layers are all at the same height or radially outward of the terminal end of the carcass ply turnup. Because the axially outer chafer plies are predominately radially outward of the carcass ply terminal end, when the bead portion is subjected to strain during operation, it is the chafer ply ends that are subjected to the greater load and where crack initiation may begin, resulting in reduced bead durability. Miyazono teaches that to improve durability, the ends of the chafer plies are bent in various different embodiments while the carcass ply turnup is maintained at a single angle. This solution only works when the chafer plies terminate radially above the carcass ply, and provides no solution for a chafer-less tire or a tire wherein the chafer plies terminate radially inward of the carcass ply turnup.
The solution proposed by Miyazono would not be appreciated by those in the art for such tires as the carcass plies and the cord reinforced chafer plies act differently under tension and deflection. The carcass ply is inclined at a radial angle, extending from bead to bead and so subject to the full tension load and bending forces of the inflated, operating tire while the chafer plies are inclined at bias angles and are only in the bead area and are not subjected to the full tension and deflection of the inflated, operating tire.